To provide information on the basic process of ATP- transphosphorylation, studies are being conducted: (A) To continue the comparison of the isoenzymes from calf, rabbit, and man of ATP-creatine transphosphorylase, by physical, chemical, and kinetic means; (B) to shed light on the basic structure of the intact two-chain molecule of the ATP-creatine transphosphorylases, with especial attention to the hybrid species; (C) To elucidate the primary structures of ATP-AMP transphorphorylase from muscle (myokinase) and liver (adenylate kinase) of rabbit and calf, and of the ATP-creatine transphosphorylases (brain- and muscle-type); (D) To correlate chemical structure and enzymic function of the ATP-creatine transphosphorylases and of the ATP-AMP transphosphorylases; (E) To complete the comparison of the ATP-creatine transphosphorylases isolated from dystrophic tissues with their normal human counterparts and thereby to provide clues as to the nature of this disorder; (F) To reexplore the association-dissociation behavior of the NTP-NDP transphosphorylase (nucleoside-diphosphokinase) with attention to effects on enzyme kinetics and covalent (phosphoryl) intermediates. As part of a program on TPN-associated reactions: (A) a number of physiochemical properties of the crystalline TPN-enzyme compound have been compared with the TPN-free crystalline Glucose 6-phosphate dehydrogenase from brewers' yeast. Studies on the ligand-induced association phenomenon have been extended to its other substrates. The controlled use of EDTA 3 minus which modifies the dissociation- association equilibria of the enzyme, has permitted a simplified approach to studies on the catalytic mechanism through direct steady- state kinetic measurements on the active, two-chain enzyme species. Studies are in progress which may correlate physical changes (the association-dissociation behavior) with enzymic function and its essential side-chain groups with catalytic activity and substrate binding. (B) Studies on ale-yeast TPNH-cytochrome c reductase are being continued.